USB, short for Universal Serial Bus, is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices. It is currently developed by the USB Implementers Forum (USB IF). USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as parallel ports, as well as separate power chargers for portable devices.
Continual upgrades and improvements to USB have produced USB 2.0, USB 3.0, USB 3.1, USB Type-C and USB On-The-Go (OTG). Continuous upgrades and improvements are being made as new technologies and uses are found. USB is well-known and widely used with computers and other electronic devices. USB OTG is a specification first used in late 2001 that allows USB devices, such as digital audio players or mobile phones, to act as a host, allowing other USB devices, such as USB flash drives, digital cameras, mice or keyboards, to be attached to them. Use of USB OTG allows those devices to switch back and forth between the roles of host and client (slave). For instance, a mobile phone may read from removable media as the host device, but present itself as a USB Mass Storage Device when connected to a host computer.
USB OTG introduces the concept of a device performing both master and slave roles—whenever two USB devices are connected and one of them is a USB OTG host, they establish a communication link. The device controlling the link is called the master or host, while the other is called the slave or peripheral. FIG. 1 shows a USB On-The-Go (OTG) A device connected to a USB OTG B device using a point-to-point link (cable). The USB OTG A device 102 may be an automobile head unit, e.g., an integrated graphics display and audio system in the automobile, and the USB OTG B device 104 may be a smart phone that may have its information content displayed and controlled with the automobile USB OTG A device 102.
However, USB OTG is a point-to-point link, and inserting a USB hub between the USB OTG A device 102 and the USB OTG B device 104, as shown in FIG. 2, is not supported because a standard USB hub downstream port does not support the OTG role swapping. In a specific automotive mobile connectivity application, e.g., display screen mirroring, the USB device connected to one of the down-stream ports of the USB hub 206 is an OTG device 104. For screen mirroring to work, between the smart phone and automotive display, the mobile (smart phone) device 104 has to change roles and become a USB host. Since this functionality is not supported by a standard USB hub, there are two options: 1) not have a USB hub in-between the USB OTG A device and the USB OTG B device, or 2) Use flex hubs that allow the swapping of USB upstream and downstream ports. Option 2 is not useful because it does not solve the problem of having a USB host on a downstream (DS) port by swapping the DS port role to a upstream (US) port, and the prior US port (connected to the auto head unit 102) then becomes a DS port. But this causes the auto head unit 102 to lose connectivity to any other downstream USB devices. This is not acceptable in an automobile connectivity environment where multiple USB connected devices have to work together, and be displayed and/or controlled by the automobile display head unit 102.